This invention relates to the field of electronic devices and more particularly to devices for dissipating electrostatic charge from the human body.
Many electronic components are susceptible to damage from electrostatic discharge. Damage generally occurs when sensitive components or the circuits in which they reside are handled by an electronics worker. Extremely high electrostatic potentials can build up in the human body and may be discharged through any electronic component or circuit that the worker touches. It is, therefore, a widely followed practice to provide electronics workers with means for dissipating electrostatic charge from the body. Typically, such means are in the form of a conductive strap which is worn about the wrist and capable of making electrical contact with the body. The wrist strap is connected to a suitable ground point (ideally, a dedicated earth ground) by means of a connecting cable. In this way, a path is provided by which any static charge in the body of the wearer is conveyed to ground and thereby harmlessly dissipated. It is only necessary for the worker to wear a grounding strap on one wrist to enable him to safely handle electronic devices with either hand, since the grounding device serves to dissipate the charge from the entire body.
A problem experienced by users of grounding wrist straps is that these devices are highly susceptible to failure through loss of electrical continuity between the wrist strap and the ground point. In such event, a user relying on a failed grounding device may unwittingly damage every charge sensitive device he handles. A widely observed solution to the problem is to test a grounding wrist strap before each wearing to verify its continuity. The observance of this practice will assure that a worker does not start work with a faulty strap. However, there is no assurance that an early failure will not occur and go undetected after the worker starts working.
Functional failure of grounding wrist straps occur with relatively high frequency because the connecting cable is subjected to constant flexure (occurring with each movement of the wearer's hand) and the device necessarily must employ very small wires or other conductors in order to be reasonably flexible and comfortable to the wearer. Furthermore, connecting cables are frequently subjected to forms of maltreatment that tend to hasten failure. Typical examples of maltreatment include subjecting the connecting cable to a strong pulling force when the wearer reaches for something beyond the reach of the cable; another form of maltreatment is to "run over" the connecting cable with the wheels of a rollered chair. These abuses are particularly destructive of cables employing carbon, carbonized fibers or other nonmetallic conductors.
A simple but obviously impractical solution to the above-described problem would be for manufacturers of grounding wrist straps to provide connecting cables of more robust proportions which could withstand all such likely forms of abuse. It will be readily seen that while heavier cable might assure greater functional reliability, it would also unduly restrict the movement of the wearer's hand and must, therefore, be considered impractical.
Another problem associated with the use of wrist grounding straps occurs when the user interrupts his activity and departs his work station. In such circumstance, the user would likely either remove the grounding strap from his wrist or detach the connecting cable therefrom. A problem arises when a worker returns to the work station to resume his activity but forgets to reconnect the grounding cable to the wrist strap. It is also possible that a worker might inadvertently connect the wrist strap to a source of electrical potential rather than a ground point, which could present a great hazard to the safety of the worker.
Accordingly, it will be seen that there is a need for improvements in the construction of grounding wrist straps to provide assurance of effectiveness in use and to protect the user against hazards associated with connecting wires to the human body. The present invention addresses the aforesaid needs and provides a static control wrist strap as described below and illustrated in the accompanying drawings.